Alkaline metal cleaning compositions and process of using same



United States Patent 3,145,178 ALKALINE METAL CLEANING COMPOSITIONS AND PROCESS OF USING SAME Jean Dupr, Levittown, and Fred E. Boettner, Huntingdon Valley, Pa., assignors to Rohm & Haas Company,

Philadelphia, Pa., a corporation of Delaware No Drawing. Filed Apr. 19, 1960, Ser. No. 23,158

5 Claims. (Cl. 252-137) This application is a continuation-in-part of our application Serial No. 777,189, which was filed on December 1, 1958, and was issued as US. Patent No. 3,079,348 on February 26, 1963.

This invention relates to improvements in the art of cleaning objects, particularly those made of metal, glass, etc.

Broadly stated, the invention pertains to alkaline cleaning and, more particularly, to surfactants for use in alkaline metal cleaning baths.

An object of the invention is to improve the cleaning efficiency of alkaline metal cleaners.

Other objects of the invention will in part be obvious and will in part be disclosed hereinafter.

Alkaline cleaners are the most widely used means in industry for cleaning metal, glass, certain plastics, etc. They are primarily used to prepare metals such as steel, brass, and copper for plating, painting, enameling, rust proofing, pickling, and other operations. Such preparation includes the removal of various types of soil such as cutting oils, grinding, buffing, stamping, and drawing compounds used in various metal-forming operations, as well as rust preventatives, lubricating greases, and various forms of dirt. The alkaline cleaning solutions may be used for soaking, spraying, or electrolytic types of cleaning. Of these, the soaking or tank cleaning technique is most important because of its widespread use in industry.

In the soaking method of cleaning, the metal article to be cleaned usually is dipped in or slowly transported through a hot alkaline solution with little or no agitation present. The cleaning solutions employed generally are made of materials consisting of between about 88 to 99 percent by Weight of various alkalies, such as caustic soda, sodium metasilicate, soda ash, trisodium phosphate, and tetrasodium pyrophosphate, and from about 1 to 12 percent by weight of a surfactant. Previously, the most Widely used surfactants for this purpose have been alkylaryl sulfonates and rosin soaps. Usually, the concentration of the cleaning materials (alkali plus surfactant) in the tank or bath is maintained between 2 and percent of the cleaning solution.

As oil, grease, and other soils are caused to be separated from the part being cleaned in the tank, a scumlike layer collects at the top of the bath. If the surfactant employed is not thoroughly soluble in the hot alkaline solution, it also will tend to accumulate in this surface layer. When the accumulation of scum in the surface layer becomes so great that it tends to coat the otherwise clean part as it is withdrawn from the bath, it becomes necessary to skim the soil and undissolved surfactant from the top of the tank. Each time this is done, a considerable amount of the surfactant is removed and, of course, this tends to lower the concentration of the effective cleaning agents in the bath to a point where the operation of the bath becomes unsatisfactory much sooner than it otherwise would if such losses could be minimized or eliminated. One obvious solution to this problem is to employ only surfactants that are soluble in hot alkaline solutions.

. There are available polyoxyalkylated tert. carbinamines which are known to have a detergent effect on metal surfaces and would appear to have other requisite F 4 3,145,178 Ice Patented Aug. 18, 1964 characteristics for alkaline cleaning purposes. These compositions, which have been disclosed in copeding US. application Serial No. 632,648, now US. Patent 2,871,266, have a structure which may be generally represented by the following formula:

R1 Rz+-NH(C H O)mH s in which R R and R are alkyl groups whose total carbon atom content ranges from 7 to 23, and m is an integer of 6 to 101.

The difficulty with compounds of the above-mentioned formulas is that they lack the requisite solubility property in hot alkaline solutions, such as, for example 5 percent sodium hydroxide. It was thought. that this lack of desired solubility could be overcome by completely (or essentially so) sulfating the compound so as to obtain a product having the following formula:

in which the values for R R and R and m are the same as indicated above, and x is a monovalent cation such as an alkali metal or hydrogen. However, when a number of these compounds were sulfated, they were found to have a materially decreased cleaning efliciency notwithstanding the fact that the product was quite soluble in hot alkaline solutions. This effect appeared difficult to explain or otherwise account for, and so efforts were made to determine the mechanism of this change in cleaning performance.

In the course of the investigation which ensued, it was discovered that not all of the polyoxyalkylated tert.- carbinamines would function efficiently as metal cleaners after they had been sulfated. Specifically, the sulfated amines which proved to be useful were those having the following formula:

R1 RrNH(C2H40) SO3-X it. in which R +R +R are alkyl groups whose total carbon atom content ranges from 11 to 14, m is an integer of 6 to 101, and X is a monovalent cation such as an alkali metal or hydrogen.

A further discovery was that, of these sulfated amines which had been demonstrated to possess utility as metal cleaners, only those having a certain narrow range of ethylene oxide units, namely between 12.5 and 17.5, gave metal cleaning results which are substantially as good as the results obtained with the non-sulfated compositions. At the same time, these compounds containing the indicated narrow range of ethylene oxide units also had the added advantage of complete solubility in the hot alkaline solution and thereby eliminated the objection described above, namely, the excessive losses caused when the surface of the cleaning baths had to be skimmed to remove the scum-like layer.

The foregoing discovery, which was based on the use of amines that were believed to have been completely sulfated, has been disclosed in our application Serial No. 777,- 186, filed on December 1, 1958. As pointed out in that copending application, the compositions therein disclosed have the further advantage of complete solubility in the hot alkaline solution and thereby avoid excessive losses caused when the surface of cleaning baths had to be skimmed to remove the scum-like layer.

We have now found that the degree of sulfation of the described sulfated polyoxyalkylated tert.-carbinamines also has a marked effect on the cleaning efficiency of those otherwise excellent compositions. When less than 75 percent sulfated, the compositions are not compatible with strong alkali, such as a hot 5 percent sodium hydroxide solution. When more than 85 percent sulfated, the cleaning 6111C1I1CY of the compositions is considerably diminished. Thus, it is essential, for maximum performance, that the polyoxyalkylated tert.-carbinamines be sulfated between about 75 to 85 percent.

In actual practice, our preferred composition is an alkali metal salt, generally sodium salt, of the tert. carbinamine ethylene oxide sulfate. Such compounds are completely soluble in 5 percent sodium hydroxide at temperatures of O-100 C. They are also soluble in concentrations such as 10 percent caustic, although not throughout this entire temperature range.

Of course, it should be understood that the sulfated amines defined above need not be present in the pure secondary amine form as indicated. For example, it is quite possible that mixtures of such secondary amines and even some tertiary amines will be present, possibly as a by-product of the method of preparing the secondary amines. The presence of the tertiary amines will in no Way interfere with the effectiveness of the single or mixed secondary amines as alkaline cleaning agents when the cleaner is prepared and used as disclosed herein.

Example 1 describes in detail the alkaline metal cleaning test which was employed to establish the utility of the present invention. Following Example 1, Table I lists a series of tert.-carbinamine ethylene oxide compounds which have been sulfated in varying amounts from to 100 percent. Also indicated for each of these compounds is the cleaningefliciency index as determined by the method described below. In this series, the ethylene oxide content has been maintained at 15.0 units, this being the amount present in one of the best of the completely sulfated compositions in accordance with the invention disclosed in our above-mentioned copending application. The actual conditions of test were made more severe than the ones which were employed in our other case in order to more sharply delineate the differences in cleaning effectiveness. This was done primarily by using less of the surfactant in the cleaning solution than the concentrations described in the examples in our other application.

EXAMPLE 1 The following test method was used for evaluating the comparative efficiencies of various alkaline metal cleaners. The method was adapted from a procedure used throughout the industry and which is described by S. Spring, H. Forman, and L. Peale in Method of Evaluating Metal Cleaners, Ind. and Eng. Chem., Analytical Edition, Vol. 18, No. 3, pp. 201-204 (1946). Briefly, the test consists of carefully cleaning thin SAE No. 1010 steel panels (3" x 3") and uniformly coating them with a thin film of bright-stock mineral oil, which is drained for one hour at 35 C. The coated panel is then rotated for 5 minutes at 30 rpm. in a 1000 m1. beaker of the solution being tested. That solution, which is maintained at a temperature of 82i2 C. in an oil bath, contains 0.07 percent active surfactant and 5 percent of a heavy duty alkaline cleaner consisting of 30 parts caustic soda, 35 parts soda ash and 30 parts sodium metasilicate pentahydrate.

Following this period of alkaline cleansing, the panel is rinsed in an overflowing beaker of warm water which is approximately 40 C., allowed to drain in air for 20 seconds, and then subjected to a light spray of deionized water for approximately seconds on each side. Any area on the panel which is still coated with residual oil will exhibit readily visible droplets which are termed water breaks. On clean areas, a continuous water film will be observed. By means of a transparent plastic sheet which is the size of the test panel, and which has been ruled olf into 100 squares of uniform dimensions, it is possible to determine the percentage of surface area which does not show any Water breaks. This value represents an index of the cleaning efliciency of the alkaline cleaner which has been used. Three such panels are run, readings taken for each side of each panel, and the average of the six sides is considered to represent the cleaning efiiciency index for the particular cleaner composition being tested. For the particular oil and concentration of surfactant used, etc., the minimum limit of acceptability has arbitrarily been set at 70 percent, this being a level of cleaning efiiciency which has been found to represent a minimum of acceptability in a number of typical industrial applications.

Employing tests such as described above for each of the cleaning compositions, which differed from one another only by the degree of sulfation of the amine surfactant which was included, results obtained were as indicated in Table I which follows:

Table I t-Alkyl Amine (EO)15 Percent Sulfated Cleaning Efliciency (Percent) 1 Norm-The surfactants employed were sulfated, polyethoxylated t-alkyl amines, the amines being a commercially available mixture in the ranges t-O12-l5HZ5-31NH2. The surfactants were all in the sodium form and the number of ethylene oxide units was 15. Their formulas, therefore, were t-O1215 Z531NH( 2 4O)l5 3 Similar data is obtained with the compounds which are exactly the same except for the ethylene oxide content which is varied from 12.5 to 17.5 units. Corresponding data is also obtained with compounds which are the same except that, instead of using the mixture of amines, the amine which is polyethoxylated and sulfated is one in the range Of t-C1 H 5NH t0 t-C15H31NH2.

It is readily apparent from the data in the table that the polyoxyalkylated t-carbinamines which, prior to sulfation, have excellent metal cleaning abilities when used in combination with strong alkalies are: (1) not compatible with strong alkali (and therefore unsatisfactory products) When sulfated below percent, because their incompatibility with the alkali causes surface loading and resultant excessive losses of the cleaner; (2) satisfactory cleaners (in combination with strong alkali) when sulfated between 75 and percent; and (3) unsatisfactory cleaners (with strong alkali) when sulfated over 85 percent and only a relatively small percentage of the surfactant is employed. A further indication of the comparative effectiveness of the present invention may be had from the fact that a commercially available alkyl aryl sulfonate, which heretofore had been considered to be among the finest surfactants known for alkaline metal cleaning applications, only rated a 13 percent cleaning efficiency index under identical test conditions.

The various amines described above can be prepared by procedures similar to that disclosed in US. application Serial No. 632,648 and may be sulfated by any of several well-known methods, using sulfuric acid, sulfur trioxide, chlorosulfonic acid, or other suitable sulfating agents. In Examples 2 and 3 are described preparations of two amines by a suitable process (the latter being the polyoxyethylene adduct of the amine produced in the former example). In Examples 4 and 5 are described typical preparations of a sulfated amine in accordance with the present invention.

EXAMPLE 2 In a suitable reaction vessel, there were combined 500 g. (2.54 mols.) t-dodecylamine, 45.8 g. (2.54 mols.) water and g. methanol. This mixture was heated to 80 C. and 139 g. (3.05 mols.) of ethylene oxide was added at 8085 C. over a period of 2 to 8 hours. At the end of this time, the product was isolated by distillation to remove the methanol and water. The yield of product (N(t-dodecyl)ethanol amine) amounted to 618.2 g. and had a neutral equivalent of 246.8. This was equivalent to N-(t-dodecyl)amine combined with 1.18 mols. of ethylene oxide. This neutral equivalent indicated that the product contained a small amount of the diethanol amine.

EXAMPLE 3 In an appropriate reaction vessel, there were combined 402.3 g. N-(t-dodecyl)ethanol amine (from above), having a neutral equivalent of 246.8, with 989.7 g. ethylene oxide in the presence of 1.6 g. powdered potassium hydroxide at 140-180 C. When the reaction was complete, the catalyst was neutralized by the addition of a strong acid. The isolated product amounted to 1392.2 g. of a light yellow liquid which tended to solidify on standing at room temperature. This product (t-dodecylamine-ethyleneoxide had a neutral equivalent of 855.5 which was equivalent to t-dodecylamine combined with 15 mols. of ethylene oxide.

EXAMPLE 4 In a suitable reaction vessel, there were combined 213.5 g. (0.25 mol.) t-alkylaminopolyoxyethylene (from Example 3 above) with 62.5 g. (0.625 mol.) 98% sulfuric acid, at a temperature of 6065 C. over a two-hour period. At the end of this time, there was mixed with this reaction mixture 51 g. (1.27 mols.) NaOH dissolved in 600 cc. of water. After separation of the excess sodium sulfate the product (237 g. of t-alkylamino-polyoxyethylene sulfate) was isolated as a pale amber, viscous liquid (viscosity 5,120 cps.). Analysis of this product gave results indicating that the material was 77.0% sulfated.

This product was soluble in boiling 5% sodium hydroxide and soluble up to 62 in 7% sodium hydroxide.

EXAMPLE 5 This preparation was carried out exactly as in Example 4 using 449.6 g. t-alkylamino-polyoxyethylene (0.5 mols.) 138 g. (1.375 mols.) 97.6% H 80 and 90 g. (2.25 mols.) NaOH dissolved in 475 g. water. The yield of the product (t alkylamino polyoxyethylene sulfate), a pale amber viscous liquid, was 475 g. (viscosity=5,860 cps.). Analysis of this product indicated that it was 85% sulfated.

This product was soluble in boiling 5% NaOH and soluble up to 75 C. in 7% aqueous NaOH.

It will be apparent to anyone skilled in the alkaline cleaner art that certain variations from the compositions and methods set forth above by way of illustration are readily feasible without departing from the scope of the present invention. For example, any of the sulfated polyoxyalkylated tert.-carbinamines described in our previously mentioned copending application will certainly be suitable. Further, although the specific examples described a typical alkaline cleaning composition made with sodium hydroxide, other alkalies of high pH may be employed. Nor must the percentages of the alkali and surfactant be limited to the 5 percent and 0.07 percent, respectively, that were employed by way of illustration in the examples. The surfactant which is the subject of the present invention is readily soluble in lower or higher concentrations of alkali and will, within the stipulated ranges of ethylene oxide content and degree of sulfation, perform with comparable efficiency in the cleaning of metal and other surfaces. Moreover, the amounts of surfactant may be varied with a proportionate effect on cleaning efliciency. Still other modifications are possible, all obviously within the scope of the following claims.

We claim:

1. A cleaning composition consisting essentially of about 8899% by weight of a mixture of a salt from the class consisting of alkali metal hydroxides, silicates, carbonates, and phosphates, the alkali metal being selected from the group consisting of sodium and potassium, and about 1 to 12 percent by weight of a mixture of at least one each of sulfated and unsulfated t-carbinamine polyoxyethylene compounds, the alkyl groups in each of the amino compounds having a total of about 11 to 14 carbon atoms, the number of oxyethylene units per amine unit present being in the range of from 12.5 to 17.5, and the proportion of sulfated to unsulfated compounds being from about to percent of the former to about 25 to 15 percent of the latter.

2. The composition of claim 1 in which the sulfated t-carbinamine polyoxyethylene compound has a monovalent cation selected from the group consisting of hydrogen and the alkali metals.

3. The composition of claim 1 in which the sulfated t-carbinarnine polyoxyethylene compound is a mixture selected from the group consisting of compounds in the range of and the unsulfated t-carbinamine polyoxyethylene compound is a mixture selected from the group consisting of compounds in the range of the values for m in all four formulas being about 12.5 to 17.5, and X in the first two formulas being a monvalent cation which is a member of the class consisting of H and the alkali metals.

4. A cleaning solution consisting essentially of water and from about 2 to about 10 percent of a mixture of alkali and surface active materials, said mixture consisting of about 8899 percent by weight of a salt from the class consisting of alkali metal hydroxides, silicates, carbonates, and phosphates, the alkali metal being selected from the group consisting of sodium and potassium, and about 1 to 12 percent by weight of a mixture of at least one each of sulfated and unsulfated t-carbinamine polyoxyethylene compounds, the alkyl groups in each of the amino compounds having a total of about 11 to 14 carbon atoms, the number of oxyethylene units per amine unit present being in the range of from 12.5 to 17.5 and the proportion of sulfated to unsulfated compounds being from about 75 to 85 percent of the former to about 25 to 15 percent of the latter.

5. In the process of cleaning metal surfaces involving the removal of soils therefrom by treatment with a hot aqueous alkaline cleaning composition, the improvement which consists of carrying out the metal cleaning operation essentially by means of the solution of claim 4 main tained at hot temperatures up to about C.

References Cited in the file of this patent UNITED STATES PATENTS 1,970,587 Schoeller et al. Aug. 21, 1934 2,314,285 Morgan Mar. 16, 1943 2,584,017 Dvorkovitz et al. Jan. 29, 1952 2,871,266 Riley Jan. 27, 1959 OTHER REFERENCES Jelinek et al.: Nonionic Surfactants, in Textile Research Journal, volume 24, No. 8, August 1954, pages 765-778. 

1. A CLEANING COMPOSITION CONSISTING ESSENTIALLY OF ABOUT 88-99% BY WEIGHT OF A MIXTURE OF A SLAT FROM THE CLASS CONSISTING OF ALKALI METAL HYDROXIDES, SILICATES, CARBONATES, AND PHOSPHATES, THE ALKALI METAL BEING SELECTED FROM THE GROUP CONSISTING OF SODIUM AND POTASSIUM, AND ABOUT 1 TO 12 PERCENT BY WEIGHT OF A MIXTURE OF AT LEAST ONE EACH OF SULFATED AND UNSULFATED T-CARBINAMINE PLYOXYETHYLENE COMPOUNDS, THE ALKYL GROUPS IN EACH OF THE AMINO COMPOUNDS HAVING A TOTAL OF ABOUT 11 TO 14 CARBON ATOMS, THE NUMBER OF OXYETHYLENE UNITS PER AMINE UNIT PRESENT BEING IN THE RANGE OF FROM 12.5 TO 17.5, AND THE PROPORTION OF SULFATED TO UNSULFATED COMPOUNDS BEING FROM ABOUT 75 TO 85 PERCENT OF THE FORMER TO ABOUT 25 TO 15 PERCENT OF THE LATTER. 